The recent increase in optical fiber data traffic has led to growing demand for additional capacity. One of the easiest ways to increase the fiber cable capacity is to increase the fiber count in the fiber cable. However, the size limitations often limit the fiber count.
Recently, spatial multiplexing, for example using multi-core fibers, has attracted interest due to their potential to multiply the capacity. Promising results prove that spatial multiplexing will be the next multiplexing technology. Implementing the spatial multiplexing will require many optical components for optical signal processing, such as power splitters, couplers, band pass filters, isolators, and the like. However, most of the current optical signal processing components are designed for single-core fibers and cannot be directly applied to a spatial multiplexing fiber such as multi-core fiber. The basic reason for this is that the photonic processors available today only have one degree of freedom (i.e., one spatial mode) whereas multi-core fibers have multiple (e.g., many) degrees of freedom. A straightforward way to build a photonic signal processor for a multi-core fiber using single-mode photonic signal processors is to separate the cores and then process each core individually using a dedicated single-mode photonic signal processor. This straightforward method increases the degrees of freedom, but also increases the number of required components by a factor equal to the number of cores (N). It would be desirable to avoid this multiplicity of components.